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XVII. On Barometrical Measurements*, 



To Mr. Tilloch, — Sir, 

 JM. De la Place in his Mtckanique Celeste, M. Ramond 

 in the Memoires de V Institute vol. vi., and M. Daubisson 

 in the Journal des Mines, February 1807, have recently 

 brought to perfection, the method of measuring altitudes by 

 means of the barometers. Their memoirs are highly deserv- 

 ing of being translated into English : it is at least certain, 

 however, that it would be agreeable to the geologists of this 

 country, and to those of foreign nations who make use of 

 instruments graduated in the English way, if the second of 

 the two methods of M. Ramond was reduced into the mea- 

 surements of this country. This second method has the ad- 

 vantages over the first of being the most expeditious, and at 

 the same time almost imperceptibly exact. I have under- 

 taken this task, and shall be happy to see it inserted in your 

 Journal, if you find it worthy of publication. 



The principal part of this work consisted in the reduction 

 of the table of M. Ramond ; the object of which is, to have 

 a view in calculation, to the gravity at different parallels of 

 latitude at which we take observations. His second method 

 abridges considerably his first; and, in my opinion, all an- 

 tecedent methods where exactitude was the object in view. 

 I subjoin this table calculated upon the co-efficient 10057*6 

 fathoms, which corresponds to 18393 metres, being that of 

 M. Ramond. 



You will perceive that the result of the calculation, ac- 

 cording to my reduction, gives the altitudes in fathoms in 

 place of giving them in feet as in England. In this trifling 

 change, I find two advantages : In the first place it renders 

 the calculation a little shorter; and secondly, it presents the 

 altitudes in numbers more easily fixed in the imagination 

 than more complicated numbers. In short, we cannot form 



* For this communication we are indebted to a learned foreigner now in 

 London. 



Vol. 33. No. 130. Feb. 1809. G a very 



